In touch screen configurations with certain touch sensors overlaid on a display, such as metal or metal-based touch sensors, the touch sensors may reflect light that is incident upon the touch sensors and may cause an undesirable view of the display. For instance, the user of a touch screen device may be able to see the liens of touch sensors overlaid on the display. This issue is especially prevalent when the display is dark or turned off, or in certain ambient light conditions.
Some current systems may attempt to prevent touch sensor visibility issues by depositing a dark coating on top of the touch sensors to make them less reflective. However, this may require additional material and/or equipment costs. In addition, this process may require careful control over the coating thickness to avoid losing conductivity, and thus performance, of the sensors. Furthermore, the dark coating may still be viewable, reducing the overall visual quality of the sensor and display, and certain issues of non-uniformity of the dark coating may also produce striping or banding patterns of the touch sensors over the display.
Other current systems for reducing the visibility of touch sensor patterns may include circular polarizer elements. However, circular polarizers may largely reduce the amount of light transmitted from the underlying display, for example by 50% to 60%. In addition, circular polarizers may only be used in conjunction with non-birefringent substrates (e.g., glass, cyclo-olefin polymer (COP), or cyclic olefin copolymers (COC)). Otherwise, they may cause rainbow effects in the image seen by a user of the device due to birefringence. Furthermore, circular polarizers may be relatively thick, and may be approximately 200-300 μm.
Other current systems for reducing the visibility of touch sensor patterns may include multi-layer stacks of anti-reflection coatings and index-matched coatings. These multi-layer coatings may be quite expensive, however, and may be quite thick.